Lanthionine is a nonproteinogenicamino acid with the chemical formula (HOOC-CH(NH2)-CH2-S-CH2-CH(NH2)-COOH). As the monosulfide analog of cystine, lanthionine is composed of two alanine residues that are crosslinked on their β-carbon atoms by a thioether linkage. Despite its name, lanthionine does not contain the element lanthanum.

In 1941, lanthionine was first isolated from the treatment of wool with sodium carbonate[1] and was first synthesized from cysteine and β-chloroalanine.[2] Lanthionines are found widely in nature and have been isolated from human hair, lactalbumin, and feathers. Lanthionines have also been found in bacterial cell walls and are the components of a group of gene-encoded peptide antibiotics called lantibiotics, which includes nisin (a food preservative), subtilin, epidermin (an anti-staphylococcus and -streptococcus agent), and ancovenin (an enzyme inhibitor).[3][4]

A variety of syntheses of lanthionine have been published including sulfur extrusion from cystine,[5] ring opening of serine β-lactone,[4] and hetero-conjugate addition of cysteine to dehydroalanine.[6] The sulfur extrusion method is, however, the only pathway for lanthionine that has been employed in the total synthesis of a lantibiotic.